1. Field of the Invention
This invention relates to a missing hole detector to be preferably located in a punching station at the upper turret of a conventional CNC punch press and adapted to detect missing or misplaced holes in a (e.g., sheet metal) workpiece that is supported at the lower turret of the punch press below the missing hole detector.
2. Background Art
It has long been known in the sheet metal industry to inspect 2-dimensional sheet metal parts for the presence and location of holes so that fasteners can ultimately be inserted into the holes during assembly to complete a variety of finished metal products. Manual inspection techniques have often been used which typically involve a string and a micrometer to verify the position of each hole relative to the edge of a metal part. However, where there is a multitude of holes is to be verified and/or where the holes have a very small diameter, it is a laborious and time-consuming task to have to manually check each hole and then provide an indication in the event that a hole is determined to be missing or misplaced or of insufficient size to receive a fastener.
Accordingly, automatic electro-optical and optical scanning and inspection systems have been proposed to increase the efficiency and lower the time associated with inspecting sheet metal parts for holes. In some cases, a special frame or table is required by which to subject the part to a complex set of movements. In other cases, expensive optical and/or computing equipment is necessary to make the mathematical calculations required to identify the presence and locations of holes in the parts undergoing testing. Still further, the large size of the typical automated inspection systems necessitates that correspondingly large amounts of space be set aside to perform the inspection process.
One example of an optical inspection system for automatically detecting holes in a flat metal workpiece is available by referring to U.S. Pat. No. 4,711,579 issued Dec. 8, 1987 to Blair E. Wilkinson.
What is desired is a compact, relatively low cost and easy-to-use automated device for detecting missing or misplaced holes in a sheet metal workpiece without the cost, complexity and space consumption that have heretofore been associated with conventional electro-optical and optical scanning and inspection apparatus.